This invention generally relates to high-density electrical connectors. In particular, the invention relates to high-density electrical connectors for connecting multiple circuit boards.
A particular application of the invention is the manufacture of ultrasound probes for medical applications. As the number of transducer elements in typical ultrasound probes increases and the desired size of the probe handle and other packaging decreases, there is a need to increase the density of electrical connections between the transducer elements and the probe cable. For reasons of manufacturability and economics, the transducer pallet and cable are usually built and tested as separate subassemblies, then joined. If the pallet and cable each terminate in a flexible printed circuit, then the preferred joint is a flex-to-flex bond. Such a bond comprises one or more rows of metallized connection pads on the transducer pallet flex circuit, similar row(s) of pads on the cable flex circuit, and an anisotropic conductive adhesive which, under heat and pressure, forms an electrical and mechanical bond between corresponding connection pads of the two flex circuits.
Flexible printed circuit substrates are typically made of a polyimide, such as Kapton™ (a DuPont product), with a typical thickness within the range of 25 to 75 microns. Another flexible printed circuit substrate material conventionally employed is polyester.
Electrical connection bonds between two flex circuits or between a flex circuit and a rigid circuit board are used in various situations and products, not just during the manufacture of ultrasound arrays. A major application is electrical connection to flat panel (LCD) displays for appliances, computers, and aircraft.
Two-dimensional ultrasound transducer arrays for medical diagnostic imaging are typically built with one flex circuit per row of transducer elements. Electrical connection to the transducer array typically requires connection to a stack of 30 to 60 flex circuits. In a typical conventional ultrasound imaging system, beamforming is performed inside the console and there is a one-to-one correspondence between transducer elements and coaxial conductors. For probes with very large numbers of transducer elements, however, it is desirable to perform at least a portion of the beamforming inside the probe head, e.g., by connecting groups of transducer elements to corresponding transmit and/or receive beamformer circuits. Connection between elements is easy within or parallel to the flex circuits, but difficult between flex circuits.
Historically, some transducer probe manufacturers have soldered coaxial cables directly to the transducer flex circuits, or have used a separate connector for each flex circuit. U.S. Pat. No. 6,007,490 discloses the use of a solderless connection for connecting and disconnecting flex circuits inside an ultrasonic transducer probe. The connector comprises a cover section and a receiver section that compress the ends of two flex circuits together. Means for aligning the flex circuits are incorporated in the cover and receiver sections, which are fastened together to hold the compressed ends of the flex circuits in place. Multiple flex circuits can be electrically connected in this way. One embodiment disclosed in U.S. Pat. No. 6,007,490 comprises a flex circuit with exposed conductors on both sides connected to respective flex circuits on opposing sides.
U.S. Pat. No. 5,160,269 discloses a connector system for interconnecting single or multiple pairs of flex circuits. A single pair of clamping bodies interconnects the respective ones of multiple pairs of electrical conductors (in the form of conductor traces carried on respective pairs of flexible substrates) by pressing the flex circuits together between slender fluid-filled flexible bladders held in channels defined in the confronting sides of the clamping bodies. Alignment pins keep the flex circuits and clamping bodies aligned properly with each other, and alignment portions of the flex circuits correspond in thickness to that of the electrically interconnecting portions, to keep the flex circuits and clamping bodies parallel with each other. The clamping bodies are urged toward one another by clamping screws.
The assignee of U.S. Pat. No. 5,160,269 subsequently developed and sold a clamp connector for use with two-dimensional ultrasonic transducer arrays. The clamp connected each transducer flex circuit to one similar cable flex circuit. Coaxial conductors were soldered to the cable circuit; the transducer circuits were embedded in the transducer. All pairs of flex circuits were stacked together within the single clamp. The clamp provided a way to make a simple, reworkable one-to-one connection between many flex circuits at one time.
There is a need for a connection scheme that would allow elements (e.g., transducer elements) connected to one printed circuit board (flexible or rigid) to be connected to elements connected to another printed circuit board (flexible or rigid). There is also a need for a connection scheme that would increase the density of connections, e.g., by allowing more than two circuit boards to be connected to one end of a single circuit board.